Influence of microcystins-LR (MC-LR) on autophagy in human neuroblastoma SK-N-SH cells

Transgenerational effects of extracts containing Microcystin-LR exposure on reproductive toxicity and offspring growth inhibition in a model organism zebrafish

Cyanobacteria cell lysates release numerous toxic substances (e.g., cyanotoxins) into the water, posing a serious threat to human health and aquatic ecosystems. Microcystins (MCs) are among the most abundant cyanotoxins in the cell lysates, with microcystin-LR (MC-LR) being one of the most common and highly toxic congeners. In this study, zebrafish (Danio rerio) were exposed to different levels MC-LR that from extracts of Microcystis aeruginosa. Changes in the MC-LR accumulations, organ coefficients, and antioxidant enzyme activities in the zebrafish were analyzed. Transgenerational reproductive toxicity of MC-LR in the maternal and paternal generations was further investigated, as well as the influences of extracts containing MC-LR exposures of the F1 on the growth of zebrafish. The study found that high levels of MC-LR could be detected in the major organs of adult zebrafish, particularly in spleen. Notably, concentration of MC-LR in the spermary was significantly higher than that in the ovarium. MC-LR could induce oxidative damage by affecting the activities of catalase and superoxide dismutase. Inherited from F0, MC-LR led to impaired development in the F1 generation. Difference in offspring survival rates could be observed in the groups with different MC-LR levels of maternal and paternal exposures. This study reveals transgenerational effects of MC-LR on the reproductive toxicity and offspring growth inhibition to the aquatic organisms, which should be emphasized in the future ecological risk assessment.

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

Microcystin-LR-induced autophagy via miR-282-5p/PIK3R1 pathway in Eriocheir sinensis hepatopancreas

With the intensifying climate warming, blue-green algae blooms have become more frequent and severe, releasing environmental hazards such as microcystin that pose potential threats to human and animal health. Autophagy has been shown to play a crucial role in regulating immune responses induced by environmental hazards, enabling cells to adapt to stress and protect against damage. Although microcystin-LR (MC-LR) has been identified to affect autophagy in mammalian, its impact on aquatic animals has been poorly studied. To investigate the toxicological effects of MC-LR in aquatic ecosystems, we constructed a microRNA profile of acute MC-LR stress in the hepatopancreas of the Chinese mitten crab. Interestingly, we found the MC-LR exposure activated autophagy in the hepatopancreas based on the following evidence. Specifically, mRNA expression level of ATG7, Beclin1 and Gabarap was significantly up-regulated, autophagy regulatory pathways were significantly enriched, and numerous autolysosomes and autophagosomes were observed. Additionally, we found that miR-282-5p and its target gene PIK3R1 played important regulatory roles in autophagy by in vivo and in vitro experiments. Overexpression of miR-282-5p mimicked MC-LR-induced autophagy by inhibiting PIK3R1 expression, while miR-282-5p silencing inhibited autophagy by promoting PIK3R1 expression. Altogether, our findings suggest that MC-LR increases miR-282-5p, which then targets inhibition of PIK3R1 to stimulate autophagy. This study focused on the stress response regulatory mechanisms of juvenile crabs to toxic pollutants in water, offering a potential target for alleviating the toxicity of MC-LR. These findings lay a foundation for reducing the toxicity of MC-LR and environmental hazards in organisms.

Liver dysfunction and energy storage mobilization in traíra, Hoplias malabaricus (Teleostei, Erythrinidae) induced by subchronic exposure to toxic cyanobacterial crude extract

Microcystins (MC) are hepatotoxic for organisms. Liver MC accumulation and structural change are intensely studied, but the functional hepatic enzymes and energy metabolism have received little attention. This study investigated the liver and hepatocyte structures and the activity of key hepatic functional enzymes with emphasis on energetic metabolism changes after subchronic fish exposure to cyanobacterial crude extract (CE) containing MC. The Neotropical erythrinid fish, Hoplias malabaricus, were exposed intraperitoneally to CE containing 100 μg MC-LR eq kg^-1 for 30 days and, thereafter, the plasma, liver, and white muscle was sampled for analyses. Liver tissue lost cellular structure organization showing round hepatocytes, hyperemia, and biliary duct obstruction. At the ultrastructural level, the mitochondria and the endoplasmic reticulum exhibited disorganization. Direct and total bilirubin increased in plasma. In the liver, the activity of acid phosphatase (ACP) increased, and the aspartate aminotransferase (AST) decreased; AST increased in plasma. Alkaline phosphatase (ALP) and alanine aminotransferase (ALT) were unchanged in the liver, muscle, and plasma. Glycogen stores and the energetic metabolites as glucose, lactate, and pyruvate decrease in the liver; pyruvate decreased in plasma and lactate decreased in muscle. Ammonia levels increased and protein concentration decreased in plasma. CE alters liver morphology by causing hepatocyte intracellular disorder, obstructive cholestasis, and dysfunction in the activity of key liver enzymes. The increasing energy demand implies glucose mobilization and metabolic adjustments maintaining protein preservation and lipid recruitment to supply the needs for detoxification allowing fish survival.

Inhibition of endoplasmic reticulum stress-related autophagy attenuates MCLR-induced apoptosis in zebrafish testis and mouse TM4 cells

Microcystin-leucine arginine (MCLR), a widespread environmental contaminant produced by cyanobacteria, poses a severe threat to the male reproductive system. However, the mechanisms of MCLR-induced testis injury accompanied by autophagy are still obscure. This study aimed to investigate the effects of MCLR on autophagy and apoptosis on the male reproductive system and its mechanism both in vitro and in vivo. MCLR caused damage to the testis of zebrafish, resulting in decreased hatching and growth retardation in the offspring. It also remarkably enhanced autophagic flux by elevating the expression of LC3BII, ATG5, and ATG12 proteins. The autophagic flux was also confirmed through the formation of autophagosomes in the ultrastructure of the zebrafish testis and the accumulation of LC3-positive puncta in zebrafish testis and mouse TM4 cells. Further evaluations revealed that inhibition of autophagy by 3-methyladenine (3-MA) significantly attenuated MCLR-induced apoptosis. This finding indicated that autophagy plays an essential role in cell death in the male reproductive system. Besides, inhibiting endoplasmic reticulum (ER) stress using 4-phenylbutyrate (4-PBA) remarkably blocked autophagy and partially suppressed apoptosis in TM4 cells induced by MCLR. This phenomenon suggested that ER stress-related autophagy was involved in MCLR-induced apoptosis. This study reveals crosstalk between ER stress and autophagy via the PERK/eIF2α/ATF4 signaling pathway. It further suggests that ER stress-related autophagy contributes to MCLR-induced apoptosis and injury in the male reproductive system. These findings provide a novel insight into MCLR-induced impairments of the testis.

Nitrogen Fertilization. A Review of the Risks Associated with the Inefficiency of Its Use and Policy Responses

Nitrogen (N) is a key input to food production. Nearly half of N fertilizer input is not used by crops and is lost into the environment via emission of gases or by polluting water bodies. It is essential to achieve production levels, which enable global food security, without compromising environmental security. The N pollution level expected by 2050 is projected to be 150% higher than in 2010, with the agricultural sector accounting for 60% of this increase. In this paper, we review the status of the pollution from N fertilizers worldwide and make recommendations to address the situation. The analysis reviews the relationship between N fertilizer use, N use efficiency, no-point pollution, the role of farmer management practices, and policy approaches to address diffuse pollution caused by N fertilization. Several studies show a lack of information as one of the main hurdles to achieve changes in habits. The objective of this study is to highlight the gravity of the current global non-point pollution as well as the need for a communication effort to make farmers aware of the relationship between their activity and N pollution and, therefore, the importance of their fertilizer management practices.

Identification and characterization of the dominant Microcystis sp. cyanobacteria detected in Lake Dong Ting, China

The presence of cyanobacteria in drinking water, aquatic foods and bathing water has created a significant major problem to global public health as these toxins induce damage in various organ including liver, cardiovascular, intestinal and central nervous systems. Although the morphologic, phylogenetic and toxicogenetic characteristics of cyanobacteria were identified in several lakes in China, many freshwater sources such as Dong Ting Lake, Hunan Province, China remain to be determined. Since the presence of these cyanobacteria may potentially affect human health, the aim of this study was to isolate, identify and characterize the most frequent occurring bloom-forming cyanobacteria in Dong Ting Lake, Hunan Province, China, which can provide information on the safety of utilization of this water source for drinking water, agriculture and recreation. Samples collected from the surface water of Dong Ting Lake were subjected to serial dilution in the lab for morphological analysis. Data demonstrated the morphological features were 2-5 µm diameters with rounded shapes and green color resembling Microcystis sp. The isolated cyanobacterial strain obtained from surface water samples in Dong Ting Lake was termed Microcystis sp. YFM2. The MC concentration was detected by enzyme-linked immunosorbent assay (ELISA) and found to be 92.88 µg/10⁷ cells in Microcystis sp. YFM2. By polymerase chain reaction (PCR) results indicated that Microcystis sp. YFM2 isolated from Dong Ting Lake contained synthetase genes (mcyA-C). Our findings indicated that the dominant cyanobacteria Microcystis sp. YFM2 isolated from the freshwater Dong Ting Lake demonstrated morphologic, phylogenetic and toxicogenetic properties resembling a toxin generating cyanobacterium. Based upon this knowledge, it is essential to monitor the use of this Lake for future domestic, agricultural and recreational purposes.